1. Field of the Invention
This invention relates to an automatic focusing camera having an automatic distance-measuring and focusing means and more particularly to an automatic focusing camera to which an optical viewfinder system and an optical distance measuring system are arranged separately from an optical photographic taking lens system.
2. Description of the Prior Art
Among the above-mentioned automatic distance-measuring and focusing means (hereinafter called an auto-focus means or an AF means) being used in an automatic focusing camera, a passive AF system means and an active AF system means have generally been used. In the passive AF system, an incident light from a subject is received by a light-receiving element, a distance is measured in a triangular surveying method, and a focus is adjusted according to the corresponding distance measuring signal.
Meanwhile, in an example of the active AF system means, the fundamental pattern is that an infrared ray is emitted from a part of a camera to a subject and the infrared ray reflected therefrom is focused upon condensing on a light-receiving unit so as to read the distance, perceiving that a focused point of the infrared ray deviates a little from the distance to the subject. Such an infrared active AF system as described above is characterized in that an automatic distance measurement is capable even when taking a photograph of a dark subject, though it is somewhat unsatisfactory to focus on the infinity. An ultrasonic projection system is also included in this category of active AF system.
FIGS. 1, 2 are schematic front views, respectively, of a conventional embodiment of the so-called auto-focus camera equipped with an automatic distance-measuring and focusing means of the described active AF system.
In FIG. 1, the described distance-measuring means 3 of active AF system is arranged above taking lens 2 which is located in a predetermined position of camera body 1 and further viewfinder 6 is arranged to the right (or the left) of distance-measuring means 3. Distance-measuring means 3 comprises light-projection means 4 comprising a light-emitting diode and a projection lens and light-receiving means 5 comprising a phototransistor or a photodiode and a condenser lens. By a distance-measured signal generated by this distance-measuring means 3, an electronic or mechanical auto-focus mechanism is operated so as to complete a proper photographing, conjointly with an exposure adjustment.
FIG. 2 illustrates that distance-measuring means 13 equipped with light-projecting means 14 and light-receiving means 15 is arranged vertically to the right side of taking lens 12 of camera body 11 and viewfinder 16 is further arranged to the right-most of the camera body 11. Cameras of this type are characterized in that the size of camera body may be made shorter in height and longer side to side.
In the conventional auto-focus cameras of this kind, the distance between taking lens 2 or 12 and viewfinder 6 or 16 is long and, therefore, the visual field of the taking lens does not coincide with that of the viewfinder, that is, a parallax is caused. Especially in a close-up photography, it must be careful because the parallax will become larger.
FIG. 3 is a schematic diagram of an optical path illustrating the parallax described above. Wherein, E is a distance between taking lens 2 having focal length f and viewfinder 6; and e is a parallax at focused point Q of subject point P at distance l ahead of taking lens 2. Parallax e is indicated by following Formula ##EQU1##
As indicated in the Formula, the greater parallax e is, the longer distance E is or the shorter distance l is. Therefore, when parallax e becomes greater, a subject visible in the visual field of a viewfinder cannot be within the visual field of a taking lens. When taking a photograph with a camera having a great parallax, a part of a subject image is cut out of the print thereof. To avoid this trouble, conventional cameras are so designed as to make the viewfinder visual field 30% to 10% smaller than the picture field taken through a taking lens. However, if the ratio of the viewfinder visual field to the picture field is made excessively smaller, the difference between the viewfinder visual field area and the actual picture frame area becomes greater, that is not desired from the viewpoint of picture composition.
FIG. 4 is a diagram of optical path illustrating the relation between a viewfinder visual field and a picture field taken through a taking lens in the cases of photographing far and near. In this drawing, P.sub.1 is a visual field taken through the taking lens when taking picture at a long distance l.sub.1 ; V.sub.1 is a viewfinder visual field; P.sub.2 is a visual field of the taking lens at close distance l.sub.2 ; and V.sub.2 is a viewfinder visual field.
FIGS. 5 (a), 5 (b) illustrate, respectively, the areas on the camera side at a long distance l.sub.1 and at close distance l.sub.2. FIG. 5 (a) illustrates a superposition of actual picture field p.sub.1 on a film to which subject P.sub.1 is photographed at a prescribed long distance l.sub.1 with viewfinder eyepiece visual field v.sub.1 through which viewfinder objective visual field V.sub.1. In this state, p.sub.1 and v.sub.1 have one and the same axis and coincide with each other, therefore, any parallax is not caused. FIG. 5 (b) illustrates a superposition of actual picture frame area p.sub.2 when subject P.sub.2 is photographed at close distance l.sub.2 with viewfinder eyepiece visual field v.sub.2. As illustrated in FIG. 5 (b), eyepiece visual field v.sub.2 does not meet with actual picture field p.sub.2 and a large parallax is therefore caused. In this case, p.sub.1 is almost the same as p.sub.2.
In the meanwhile, in an automatic focusing camera, an auto-focus frame (hereinafter called an AF frame) is provided to the approximate center of the viewfinder visual field of the camera.
In an active AF system, parallel beams having generally the angles of 3.degree. to 10.degree. of fine infrared rays are projected from the window of a light-projecting means such as an infrared projecting means of a distance-measuring means, and when the beams hit distance-measuring subject area F.sub.1 nearly in the center of subject P.sub.1, then an invisible bright spot is illuminated. The infrared rays reflected from F.sub.1 enter into the window of the light-receiving means of a camera, and an image is formed on the light-receiving spot of a phototransistor or a photodiode through a condenser lens.
When measuring at a given long-distance l.sub.1, as shown in FIG. 5 (b), the distance is measured in the center portion F.sub.1 of objective visual field V.sub.1 because the described AF frame f.sub.1 in the viewfinder visual field is provided nearly to the center of eyepiece visual field v.sub.1.
Next, when photographing subject P.sub.2 at close distance l.sub.2, as shown in FIG. 5 (b), eyepiece visual field v.sub.2 shifts to the upper left side of the described v.sub.1 and AF frame f.sub.2 of v.sub.2 is accordingly shifted together with the shifting of the center of v.sub.2. In other words, when photographing at close distance, a distance is measured in the portion of the shifted objective visual field F.sub.2 corresponding to eyepiece visual field f.sub.2, but is not measured in the center of an actual picture-taking field corresponding to eyepiece visual field f.sub.1. In the drawing, the distance measuring portion overlapped in common by f.sub.1, f.sub.2 is the small area with oblique lines and the other areas do not meet with each other and cause measurement errors.
The above description relates to the correlative shifts (i.e., a parallaxes between viewfinder eyepiece visual fields v.sub.1, v.sub.2 and distance-measuring AF frames f.sub.1, f.sub.2 with respect to actual picture-taking fields p.sub.1, p.sub.2, respectively, in the case that the optical axis of the viewfinder and that of the distance-measuring projection light are nearly in alignment with each other. However, generally, the optical axis of a viewfinder is separated with an interval from a distance-measuring optical axis. In this case, there still causes a parallax, as described above, because of the difference between the optical axis of the viewfinder and that of the distance-measuring projection light, when at close distance. Even if a photographer aims at a subject and could catch the portion of the subject to be measured in the AF frame of the viewfinder, an infrared projection spot actually hits from a distance-measuring means to a position slightly shifted from the described portion of the subject to be measured because of the parallax, and the distance is measured by receiving the reflected infrared rays from the shifted position. For example, when photographing a subject at close distance after catching the subject in a measuring portion of AF frame, distance-measuring infrared beams reach the background directly, so that the distance-measuring means erroneously judges as if it were a long distance, and the picture comes out of focus.